JP2005526238A - Opaque additive that blocks stray light in a flow cell for TEFLON (registered trademark) AF light guidance - Google Patents

Abstract

The present invention is directed to the use of a light-absorbing wall material 4 to eliminate stray light paths in light-guided structures such as those used for HPLC absorbance detection. More specifically, the present invention relates to carbon-mixed Teflon AF or “black Teflon (registered trademark) for all or part of the walls of the light induction flow cell 2 adapted for use in HPLC absorbance detection. (Trademark) AF ”.

Description

  The present invention relates generally to the use of light absorbing wall materials to eliminate stray light paths in light-guided applications such as high performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE) spectroscopy.

  A light absorption detection system generally has four basic components: a light source, a means for selecting the wavelength to be used, a light guiding vessel (flow cell) (usually a sample to be analyzed and a hollow or capillary tube through which light passes). And a photodetector for measuring the amount of light transmitted through the flow cell. Large light throughput is achieved when light is guided along a capillary in the same way that light is guided along an optical fiber.

に従って求められる。ここで、Ｉ_０は、フローセルに透明な流動層（ｍｏｂｉｌｅ ｐｈａｓｅ）を充填した時のフローセルを出る光であり、Ｉは、分析物が存在する時のフローセルを出る光出力である。ｂは、フローセルの経路長（慣例的に、センチメートルで表される）であり、ｃは、Ｍまたはモル／リットルの分析物濃度であり、εは、ｃｍ⁻１（モル／リットル）⁻１の単位で表されるモル吸光係数である。Ａは吸光度（吸光度単位（ａｕ）で表される無次元数）である。 The flow cell must be composed of materials that are resistant to solutions encountered in liquid chromatography or CE. To obtain high sensitivity for low concentrations of analyte, the cell must have high light throughput and long path length. If the amount of analyte is low and capillary separation techniques are used, the cell volume must also be small, otherwise there will be a reduction in band spread and chromatographic resolution. The transmittance T of light passing through such a system filled with a light-absorbing sample is the Beer's law, ie

As required. Here, I ₀ is the light exiting the flow cell when the flow cell is filled with a transparent fluid phase, and I is the light output exiting the flow cell when the analyte is present. b is the path length of the flow cell (conventionally, in centimeters), c is the analyte concentration of M or mol / liter, epsilon is cm - ^{1 (mole} / liter) ^- 1 Is the molar extinction coefficient expressed in units. A is absorbance (a dimensionless number expressed in absorbance units (au)).

The requirements for high light throughput and long path length are given by differential equation (1b).

  Δc is the lowest analyte concentration that can be detected, and ΔA is the smallest change in the corresponding absorbance that can be measured. This represents the noise at the absorbance baseline, the output of the absorbance detector.

As shown in equation (1b), to reduce absorbance noise, the optical signal I ₀ is increased and the noise in the measurement of I is reduced, ie, the signal to noise ratio (S / N) in the raw transmission measurement. Need to be larger. In a well-designed detector, shot noise proportional to the square root of the optical signal is dominant. Therefore, in order to increase the S / N, it is necessary to increase the optical throughput.

ここで、ｎ_１は液体のＲＩであり、ｎ_２はフローセルの壁のＲＩである。 The light guiding flow cell allows a small capacity cell to be constructed with high light throughput and long path length. The liquid sample is contained in a tube made of a material having a refractive index (RI) smaller than the fluid phase. Light is introduced at one end of the tube and propagates down the tube axis with multiple internal reflections before exiting at the other end. The liquid resembles an optical fiber core, and the tube material resembles cladding. Light-induced conditions, light rays incident to the liquid / wall boundary is to incident at a large incident angle than the critical angle theta _c.

Here, n ₁ is the RI of liquid and n ₂ is the RI of the wall of the flow cell.

で与えられる。ここで、ψは、空気からセルに入る光線とセルの軸の間の、誘導条件を満足する最大角である。誘導メカニズムは、全内部反射（ＴＩＲ）と呼ばれる。 The numerical aperture (NA) of the guide beam is

Given in. Here, ψ is the maximum angle satisfying the guiding condition between the ray entering the cell from the air and the cell axis. The guidance mechanism is called total internal reflection (TIR).

  Recently, it has become possible to construct a light guiding flow cell with a flow cell having an internal surface made of a common chromatographic solvent, for example, an amorphous fluoropolymer having a refractive index less than that of water.

  Light introduced along the tube axis is guided into the fluid by total internal reflection at the fluid wall boundary. Amorphous fluoropolymer materials Teflon® AF 1600 and 2400 are preferred tube materials. The reason is that these materials are transparent over the visible and ultraviolet spectra, have very low refractive indices (1.31 and 1.29, respectively) and are chemically inert. For comparison, the RI of water of the same wavelength is 1.333. All common solvents (such as methanol / water mixtures and acetonitrile) have a higher RI than water, and thus also Teflon® AF. Only pure methanol has a slightly lower refractive index than water, but is still greater than Teflon® AF. Even at different wavelengths, fluoropolymers retain the benefits of RI.

  However, a certain amount of light 18 does not enter the end section of the wall, or a certain amount of light 18 does not scatter and enter the wall from the liquid, or a certain amount of light 18 does not enter the sample fluid. It is difficult to make cells with amorphous fluoropolymer walls so that after some or all of them are bypassed, they do not enter the fluid from the walls. These abnormal light paths create a stray light background that results in inaccurate readings and limits the linearity and dynamic range of the detector that is assumed to receive only light that has passed through the liquid.

  One strategy for controlling stray light is in the opaque mask between the wall and the light, but the small diameter tubes of the HPLC and CZE instruments make alignment of these masks difficult and time consuming. A second strategy for controlling stray light provides incident light through an optical fiber having an OD that fits between the walls, but the amount of light coupled into the liquid is reduced by a geometric reduction in area.

  The difficulty of controlling stray light increases as the fluid cross section decreases. For capillary HPLC or CZE detection, a fluid channel ID of 100 μm or less is required to create a small volume flow cell with sufficient path length to maintain analytical sensitivity. In order to avoid the difficulty of controlling the stray light outlined above, there is a need for a better method of making a light guiding flow cell.

  The present invention provides an apparatus and method for controlling stray light in a container that has a small cross section and that is used in particular for light absorption measurements.

  In a preferred application, the container is a flow cell that receives the analyte from the HPLC apparatus. One embodiment is a device that receives one or more samples and measures light emitted from or refracted from the sample. The device comprises a container having a cavity for receiving a sample during the measurement process, the container comprising at least one wall in fluid contact with the sample, the wall having a refractive index that is less than the refractive index of the fluid in the sample. Having a composition. Furthermore, the wall has an absorption coefficient sufficient to significantly attenuate light propagating through the wall, the container has means for passing at least one transmitted light, and the light in the cavity is totally attenuated. It is induced in the sample by reflection. By judicious selection of the wall absorption coefficient, the attenuation of light induced through the fluid by internal reflection is only minimal. The means for transmitting the transmitted light may be an aperture, a window, a lens and an optical fiber. A preferred material for the wall is Teflon® AF fluoropolymer mixed with a black dopant such as carbon black.

Another embodiment comprises a fluid channel bounded by at least one wall, the composition of the wall having a refractive index that is less than the refractive index of the fluid in the fluid channel and significantly increasing the light propagating through the wall. It has a sufficient absorption coefficient to attenuate. The apparatus further comprises light inlets and outlets, the inlets and outlets being perpendicular to the channel and fluid inlet and outlet port axes, whereby the walls and fluids are guided by light by attenuated total reflection. Yes, the wall has a minimal absorption effect on the guided light. Wall, ultraviolet, at a wavelength in the wavelength range outside the visible, and near infrared, from 0.1 100 mm ^- having an absorption coefficient in the range 1. A preferred material for the wall is Teflon® AF fluoropolymer mixed with a black dopant such as carbon black. A carbon black concentration between 0.01% and 1% by weight of the fluoropolymer is sufficient to absorb stray light.

  Another embodiment is an apparatus that contains a liquid sample and exposes the liquid sample to light. The apparatus comprises a conduit, the conduit has a refractive index less than that of water, and when the conduit is filled with water, visible and ultraviolet light is approximately along the axis of the conduit by attenuated total reflection. It has a wall formed from an amorphous fluoropolymer that transmits without loss but has an absorption coefficient that is such that visible and ultraviolet light are absorbed almost completely in the passage through the wall of the conduit.

  A method for photometric analysis of a liquid sample with improved detection linearity has a refractive index less than that of water and has an absorption coefficient sufficient to significantly attenuate light propagating through the wall Introducing a liquid sample into a conduit having a wall made of amorphous fluoropolymer, directing light axially onto the conduit filled with the sample liquid, and detecting the light transmitted through the liquid sample with a detector. Receiving and determining the concentration of the sample in the liquid by measuring the light absorption of the sample. When light is applied axially to a conduit filled with sample liquid, the light transmitted through the liquid sample is detected and the sample concentration in the liquid is determined. Alternatively, the sample concentration can be determined using emitted fluorescence or Raman scattered light.

  The set of fluidic light-guiding flow cells is formed on a substrate made of a material having a refractive index smaller than that of the fluid and an absorption coefficient sufficient to significantly attenuate light propagating through the material. With a set of channels. A set of channel covers formed on a portion of the material having the same refractive index and absorption coefficient as the substrate material is secured to the set of channels to form a set of coated channels. At least one coated channel, or set of interconnected coated channels, has fluid inlet and outlet ports. At least one coated channel has a light source at the light entrance end and a light exit end. Thereby, the at least one coated channel and fluid induce light by attenuating total reflection, and the at least one coated channel has a minimal absorption effect on the light induced by internal reflection. The coated channel is configured as a separation column. When the output of the separation column is connected to the light guiding channel, the interconnected channel performs an analysis on the fluid passing through the interconnected channel. At this time, the light exit end is connected to a detector outside the set of flow cells.

  A common use of the present invention is in a flow cell for HPLC or CE absorbance detection, where the flow cell consists of a hollow tube made of a low refractive index material such as darkened Teflon® AF2400. The wall material is sufficiently absorbent to block light transmitted through the wall. At the same time, the absorption by the walls is low enough that light induction is almost unaffected. Teflon® AF mixed with carbon, or “black Teflon® AF”, is a material that is well suited to all or part of the walls of these light-guided flow cells for use in HPLC absorbance detection. It is.

  These and other features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Therein, like reference numerals designate corresponding parts throughout the several views.

  A light guiding structure with excellent signal-to-noise characteristics judiciously selects the absorption coefficient of the wall of the liquid container so as to minimize attenuation due to internal reflection of light guided through the liquid Can be configured in case. The container can be formed to contain a single sample as an array of single sample containers or as a flow cell capable of analyzing a sequence of samples. The principles of the present invention are discussed by way of example using a light guidance flow cell that is simple, easy to configure, minimizes stray light, and maximizes for selected volumes and path lengths. Shows the optical throughput. The small RI wall material should be sufficiently absorbent to block the stray light path (causing non-linearity between absorbance and concentration) that bypasses some or all of the liquid sample. By having no mask or optical fiber inserted into the flow cell lumen, optical throughput can be maximized.

と記述される。ここで、αは往復（ｒｅｃｉｐｒｏｃａｌ）長の単位での材料吸収係数であり、ｂは材料内を進む距離であり、端部反射損失を無視すると、Ｉ_０およびＩは材料をそれぞれ入りまた出る、光強度すなわち出力である。 A justified claim, as discussed below, is that a wall of low index of refraction is such that unwanted light entering the wall is absorbed and the desired light directed along the flow cell channel is transmitted without loss. It is possible to select a bulk absorption coefficient for the material. Absorption of light through the material is due to the Bauger / Lambert law:

Is described. Where α is the material absorption coefficient in units of reciprocal length, b is the distance traveled through the material, and ignoring end reflection losses, I ₀ and I respectively enter and exit the material, Light intensity or output.

Appropriate light blocking can be achieved if the light transmitted through the tube wall and parallel to the lumen is reduced to 1/1000 of the incident intensity within a distance of 5 mm. This substantially eliminates stray light through the bulk material. Using these parameters, equation (3) yields an absorption coefficient of α = 1.4 mm ⁻¹ . The effect of this material change on the light induction characteristics is considered below.

  When light rays are induced by total internal reflection at the boundary between the core material and the low index cladding, a small amount of light penetrates into the small index medium. If the medium with a small refractive index is transparent, the internal reflection is 100%. However, when a medium with a small refractive index absorbs light, a small amount of light wave that penetrates traps a certain amount of energy, and the process is called attenuated total reflection (ATR). Similar to this design, if the absorption is small, a relatively simple equation can be used to calculate the effective thickness of Teflon® AF through which light penetrates at each internal reflection (Harrick N. J., (See Internal Reflection Spectroscopy, Harrick Scientific Corp., Ossming, NY, 1987, p43). The effective thickness depends on the wavelength, the angle of incidence, the refractive index of the two media, and the plane of polarization. The physical orientation of the part is shown in FIG.

である。 For light polarized perpendicular to the plane of incidence, the effective thickness is

It is.

である。ここで、
ｎ_１は、媒体１（流体試料）の屈折率である。 For light polarized parallel to the entrance surface, the effective thickness is

It is. here,
n ₁ is the refractive index of the medium 1 (fluid sample).

n ₂ is the refractive index of medium 2 (Teflon® in contact with the fluid).

  θ is the incident angle of the light beam internally reflected at the boundary between the two media.

n ₂₁ = n ₂ / n ₁
λ ₁ = λ / n ₁ is the wavelength in the medium 1. λ is the wavelength in air.

  One possible application is to utilize a 5 mm long light guiding flow cell with a 100 μm ID, a 0.27 tube numerical aperture (NA), and a light beam with a wavelength of 250 nm. Rays that make a maximum angle (arcsin (NA)) with respect to the axis and reflect from the boundary at the angle closest to the critical angle will reflect about 10 times and penetrate deeper into the wall. The effective thickness of Teflon® AF through which these rays pass is the average of equations (4a) and (4b) above, assuming non-polarized light. For the worst case ray, the effective thickness is 1.4 μm per reflection, ie 14 μm for the total length of the flow cell. Using this value for b and the previously calculated value of α, the transmittance of the induced light is determined as 0.98 by equation (3). Light rays that make a small angle with respect to the axis are much more transparent. These calculations show that with such an absorption coefficient large enough to block light transmitted through the dark Teflon AF wall, the attenuation of the induced beam is negligible.

  FIG. 1 shows a single sample container 2 for measuring light after passing through a sample constructed using the present invention. The sample to be tested is placed in the cavity 6 of the container 2. A means 10 for passing light is provided in the wall 4 of the container 2 to allow light to enter (16) and exit (16 '). The means for passing light may be an aperture, window, lens, or optical fiber. Since the wall 4 is made of dark Teflon® AF, light with an angle of incidence smaller than the critical angle is guided downstream through the cavity, and some light is reflected at the end of the cavity, Measured when leaving. The light incident on the end face 11 of the wall 4 is absorbed and does not interfere with the measurement. This container can be adapted to other configurations. An array of containers 2 can be configured to test multiple samples. If the window replaces the reflective surface 8, the measurement sensor can be placed on the opposite side of the light source. Such adaptation may prove advantageous for large-scale screening of discrete samples. When the container 2 is further modified to allow the sample fluid to pass through, a flow cell as shown in FIG. 2 is formed.

FIG. 2 shows a simplified design of a flow cell made possible using the present invention. Tube 17 is a dark Teflon AF wall. The fluid under test enters at one end 18 of the tube 17 and exits at the other end 19. Incident light 16, 24 is directed at an angle within the NA of tube 17. The light source 19 is wider than the ID of the tube 17 and is aligned with the axis. Light 16 that is directed into the liquid medium having n ₁ RI is guided downstream of the cavity 15 because the incident angle θ is smaller than the critical angle. Light 24 falling outside the cavity enters the cell wall 4 and travels a short distance and is absorbed. FIG. 2 shows a single window 26 at the exit of the light guiding flow cell. This avoids aligning and aligning the optical fiber with the outlet of the flow cell, leading to improved light efficiency. The entrance to the flow cell can also be a window and the light is focused at the entrance. Light striking the wall 4 of the tube 17 is absorbed as described above. The design is simplified because a mask is no longer needed at the end of the cell. Light efficiency is maximized because the entire fluid path cross-section is flooded with light.

FIG. 3 shows the number of reflections (diamonds) made by a light wave that undergoes total internal reflection from the inner wall of a Teflon AF tube filled with water, as calculated previously, to determine the effect on transmission. ). Further, the “effective thickness” (square) of the Teflon (registered trademark) AF material through which the light passes while passing through the light guiding portion is plotted. This makes it possible to determine the attenuation of the light beam as it undergoes multiple reflections downstream of the tube. The data in FIG. 3 is plotted against the numerical aperture NA. NA determines the cone of rays entering the light guide. The most inclined light beam forms an angle sin ⁻¹ (NA) with the axis of air outside the light guiding portion. This is the stimulated light that is subject to maximum attenuation due to wall absorption and whose data is plotted in FIG.

If ten times the concentration of the black dopant is used, giving a wall absorption coefficient of α = 14 mm ⁻¹ , the worst case light transmission drops to 82%, resulting in an acceptable loss rather than a significant loss Will. This allows for a modest choice when selecting the concentration of the opaque dopant, or alternatively, the dopant absorption coefficient varies by a factor of 10 over the desired wavelength range and still meets the required criteria. Is possible.

  Preferred opaque dopants are chemically resistant to the HPLC solvent and pH range and have a spectrum that is as flat as possible over the wavelength region of interest, 200 to 800 nm. Carbon black was mixed with fused silica to create a “black crystal” that was used to block the stray light path, especially in flow cells and cuvettes used to analyze fluorescence (Hulme US Pat. No. 5,493). 405, see U.S. Pat. No. 6,106,777 to Fujita et al.). In these cells, no light induction occurred because the wall material had a higher refractive index than the analytical fluid. However, as a material that blocks transmitted light over a wide wavelength range, carbon is a good choice for this application for light-guided cells. Other materials such as finely divided metal particles may be used. Many different dopants may be used over a more limited wavelength range.

  FIG. 4 illustrates a method for constructing a flow cell incorporating the present invention. The flow cell body 42 is composed of a sealable material, such as PEEK, in multiple parts. A dark Teflon® AF 44 tube is held in part of the cell body 42. Fluid 38 enters the body via capillary tube 40 and is introduced into tube cavity 43 by channel 45 etched into metal gasket 32 between body portions 42. After passing through the tube 44, the fluid is further routed through the metal gasket 32 and out of the fluid port 34. Light 36 enters the flow cell via optical fiber 35 and passes through a tube cavity 43 filled with fluid. On the exit side of the tube 44, the window 30 allows light 46 to exit the flow cell and travel towards the sensor. It is clear that light passes along the length of the light guide tube 44. In this flow cell, the portion of the metal gasket 32 that covers the end of the tube wall 44 is not important for light blocking. The reason is that the opacity of the tube 44 wall prevents stray light from entering the fluid path.

  In one embodiment, fine carbon black is mixed with Teflon® AF2400 resin in powder form. The carbon black concentration is about 0.01 to 1%. In a preferred embodiment, the carbon black concentration is about 0.1%. With the resulting mixture, a “black” Teflon® AF tube is made by extrusion or stretching using an already well-established method. Low levels of carbon black do not significantly affect the ability to make tubes. When a “black” Teflon® AF tube is used in a light guiding flow cell, the tube blocks light from passing through the cell wall, so that the stray light cannot reach the detector at all. , No measurement error is caused.

  A “lab-on-a-chip” structure was created on a flat substrate where certain channels were fluid connections, separation columns, and reaction chambers. As a second embodiment of the present invention, a “black” Teflon® AF strip was extruded in the form of a ribbon that was several mm wide and about 1 mm thick. Using this portion as a substrate, a channel pattern is formed, for example, by hot embossing. Using two such substrates bonded together, or one substrate with an unstructured lid, a “lab-on-a-chip” structure with unique properties is created. Some channels in the chip are used as fluidic connections to other channels formed as separation columns. These can be connected to a light guide that contains the fluid created for detection. A window to the light guide is created and combined to sandwich various lengths of optical fiber to provide the required light on the chip to couple to the appropriate channel. By using an opaque “black” Teflon® AF material as the substrate, stray light is blocked and a light guiding detection channel can be constructed. Furthermore, the “black” Teflon® AF bulk material prevents any stray light from other parts of the chip from leaking light into the detection system. This improves the linearity of the detector as discussed above. By using the light blocking substrate, a plurality of light guiding flow cells can be formed on the same substrate without crosstalk.

  FIG. 5 shows a simplified diagram of a “lab on chip” made possible by the present invention. The substrate 50 is formed from “black” Teflon® AF. Channel 51 forms a fluid connection from inlet 52 to channel 54 formed as a separation column. The optical fibers 56 and 58 are combined to form part of the end wall of the light guiding channel 60 that is used to measure the absorbance of the sample passing through the channel 60. The fluid exits the structure through channel 62. On the same substrate, another light guiding flow cell allows measurement of the absorbance of the fluid passing through channel 53 to channel 67 (measurement channel). Another optical fiber 68, 70 couples to the channel 67 to form the light inlet and outlet. Because the substrate 50 is opaque, the light is limited to the two light induced measurement channels 60, 67.

  Although the use of small RI materials that block light has been discussed in the context of absorption measurements, the materials are also applicable to light-guided applications used for fluorescence and Raman detection. The opaque cell wall absorbs unwanted excitation light that enters or scatters into the cell wall.

  The material has been discussed in the context of a cuvette made of an optically transparent material stretched in the form of a cylindrical thin-walled capillary used for absorbance measurements. However, a further application of “black” Teflon® AF is to form cuvettes in containers having reflective surfaces opposite the windows / openings where light enters or containers having transparent windows opposite each other.

  It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

FIG. 3 is a simplified view of a light guiding container according to the present invention. FIG. 3 is a simplified diagram of a light guiding container in the form of a flow cell according to the present invention. 4 is a graph showing the depth of penetration of light waves into a wall according to the present invention. It is a figure of the flow cell comprised incorporating the present invention. FIG. 3 is a simplified diagram of a “love on chip” implemented using the present invention.

Claims (31)

A device for receiving one or more samples and measuring light emitted from or refracted from the sample,
A container having a cavity for receiving a sample during the measurement process,
At least one wall in fluid connection with the sample, the wall having a composition having a refractive index less than the refractive index of the fluid in the sample and greatly propagating light propagating through the at least one wall. At least one wall having an absorption coefficient sufficient to attenuate to
Comprising at least one means for transmitting transmitted light;
A device in which light in the cavity is guided into the sample by attenuated total reflection.   The device of claim 1, wherein the container has at least one fluid inlet for receiving the sample.   The device of claim 1, wherein the container has at least one fluid outlet for discharging the sample.   The device of claim 1, wherein said means for transmitting transmitted light is selected from the group consisting of an aperture, a window, a lens and an optical system.   The device of claim 1, further comprising a reflective surface facing the means for transmitting transmitted light and reflecting the light that has passed through the sample back to the means through the sample.   The device of claim 1, further comprising means for transmitting light to the sample, and a window facing the means for receiving light that has passed through the sample.   The device of claim 1, wherein the length of the cavity is 10 to 50 times the inner diameter of the cavity. The device of claim 1, wherein the wall is formed of Teflon® AF fluoropolymer.   The device of claim 8, wherein the Teflon® AF fluoropolymer is mixed with a black dopant.   The device according to claim 9, wherein the black dopant is carbon black or fine metal particles.   The device of claim 8, wherein the concentration of the dopant is between 0.01 and 0.1% of the fluoropolymer.   The device of claim 8, wherein the concentration of the dopant is about 0.1% of the fluoropolymer. A device for guiding light,
A fluid channel bounded by at least one wall, the composition of the at least one wall having a refractive index less than the refractive index of the fluid of the fluid channel and transmitting light propagating through the wall A fluid channel having an absorption coefficient sufficient to significantly attenuate;
A light inlet perpendicular to the axis of the channel;
A light outlet perpendicular to the axis;
Fluid inlet and outlet ports, whereby the wall and fluid induce the light by attenuating total internal reflection, and the wall has minimal absorption of the induced light; A light guiding device comprising a fluid inlet and outlet port.   The light guiding apparatus according to claim 13, wherein the wall is formed of a hollow tube. It said wall including ultraviolet, visible, and at a wavelength within the near-infrared wavelength range, 0.1 to 100 mm - light guiding device according to claim 13 having an absorption coefficient of ^1.   The light guiding device according to claim 13, wherein the wall is formed of Teflon® AF fluoropolymer.   17. The light guiding apparatus according to claim 16, wherein the Teflon (registered trademark) AF is mixed with a black dopant.   The light guiding device according to claim 17, wherein the black dopant is carbon black or fine metal particles.   The light guiding device according to claim 18, wherein the concentration of the black dopant is between 0.01 and 1% by weight of the fluoropolymer.   20. The light guiding device of claim 19, wherein the dopant concentration is about 0.1% of the fluoropolymer.   The light guiding device according to claim 13, wherein the device is a flow cell.   14. The light guiding device according to claim 13, wherein the fluid inlet and outlet ports are configured off the axis. An apparatus for containing a liquid sample and exposing the liquid sample to light,
The conduit is formed of an amorphous fluoropolymer having a refractive index less than that of water, and the conduit is subject to total reflection where visible and ultraviolet light attenuates when the conduit is filled with water. A device having an absorption coefficient large enough to transmit along the axis of the conduit with almost no loss so that visible and ultraviolet light is almost completely absorbed in the passage through the wall of the conduit. A method for photometric analysis of a liquid sample,
The liquid sample in a conduit having a wall made of amorphous fluoropolymer having a refractive index less than that of water and having an absorption coefficient sufficient to significantly attenuate light propagating through the wall Introducing,
Illuminating the conduit filled with sample liquid in an axial direction;
Receiving light transmitted through the liquid sample at a detector; and
Determining the concentration of the sample in the liquid by light absorption by the sample, thereby improving the linearity of detection, the method comprising determining the concentration of the sample.   The axial light is the excitation wavelength and the transmitted light is the emitted fluorescent or Raman scattered light used to determine sample concentration and sample identity, thereby undesirably scattered excitation entering the conduit 25. The method of claim 24, wherein the light is suppressed and does not reach the detector. A set of light guiding flow cells for fluids,
A set of channels formed in a substrate of the material having a refractive index less than that of the fluid and an absorption coefficient sufficient to significantly attenuate light propagating through the material;
A set of channel covers formed on a portion of the material having the same refractive index as the substrate material and an absorption coefficient sufficient to significantly attenuate light propagating through the material, The set of fixed channel covers comprises a set of channel covers, forming a set of coated channels;
At least one coated channel has fluid inlet and outlet ports configured off-axis of the coated channel;
At least one coated channel has a light source at the light entrance end and a light exit end;
Thereby, the at least one coated channel and fluid induces the light by attenuating total reflection, and the at least one coated channel has a minimal absorption effect on the light induced by internal reflection. A set of light guiding flow cells for fluids.   27. The set of light guiding flow cells of claim 26, further comprising an optical fiber coupled to at least one coated channel that provides the light source.   27. The set of light guiding flow cells of claim 26, wherein the material forming the closed channel prevents optical crosstalk between the flow cells.   27. A set of light guiding flow cells according to claim 26, wherein the at least one coated channel is configured as a separation column.   27. A set of light guiding flow cells according to claim 26, wherein at least one coated channel is configured as a fluid connection.   26. The light guide according to claim 25, wherein the substrate and the portion are formed of Teflon® AF fluoropolymer mixed with black dopant at a concentration between 0.01 and 0.1% of the fluoropolymer. A set of flow cells.

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